Changes in the electrokinetic properties of platelets during their aggregation

Abstract

The electrophoretic mobility of human blood platelets suspended in plasma or standard saline has been examined. The mobility of the human platelet in standard saline at pH 7 is −0.85 μ per second per volt per centimeter with an isoelectric point approximately at pH 3.6. Treatment of washed platelets with neuraminidase leads to about a 50% reduction in the electrokinetic charge and an increase in the isoelectric point to about pH 4.2. Approximately 1 × 10 5 molecules of sialic acid are released by this treatment per μ 2 of platelet surface. Fixation of washed platelets with acetaldehyde produces about 20% increase in the anodic mobility at pH 7, which implies the presence of a significant number of amino groups at the surface. Addition of up to 200 μg of ADP per milliliter of washed platelets suspended in saline produces no significant change in the electrophoretic mobility, whereas addition of only 1 μg ADP per milliliter of platelet rich-plasma produces about 15% decrease in the electrophoretic mobility of the platelet, which mobility, however, gradually returns to the control value after some 15 minutes. In contrast, addition of 50 μg/ml of 5-hydroxytryptamine produces a significant reduction of mobility of platelets in standard saline at pH 7, but does not alter the mobility of platelets when added to them in plasma. 5-Hydroxytryptamine does, however, exert a synergistic effect in plasma when used in conjunction with ADP. The degree of aggregation of platelets produced in plasma by the addition of ADP parallels the changes in the electro-kinetic charge which occur. The results are interpreted in relation to the hypothesis of hydrogen bonding of the adenosine moiety of ADP to specific sites at the platelet surface.